1. Field of the Invention
This invention relates to the preparation of tetrahydrofuran from at least one of maleic anhydride or succinic anhydride. More specifically, this invention relates to a single stage process for the hydrogenation of maleic anhydride or succinic anhydride in alcohol in the presence of a catalyst comprising the mixed oxides of copper, zinc and aluminum to produce high yields of tetrahydrofuran.
2. Description of the Prior Art
Tetrahydrofuran is a useful solvent for natural and synthetic resins and is a valuable intermediate in manufacture of a number of chemicals and plastics.
It is known in the art that tetrahydrofuran may be produced by a number of different methods, the more prominent among them is the dehydration of 1,4-butanediol and the catalytic hydrogenation of furan. Most tetrahydrofuran is, in fact, manufactured in a multi-step sequence starting with the reaction of acetylene and formaldehyde in the presence of a cuprous acetylide complex to form butynediol. The butynediol is hydrogenated to butanediol, which is dehydrated to tetrahydrofuran as indicated above.
In addition, tetrahydrofuran can be prepared by catalytic hydrogenation of maleic acid, fumaric acid and succinic acid, their respective anhydrides and ester derivatives, and butyrolactone.
The instant invention focuses on the production of tetrahydrofuran from maleic anhydride in the presence of an alcohol. A multi-step process for producing tetrahydrofuran from maleic anhydride is described in U.S. Pat. No. 4,584,419. In this patent the ethyl diester of maleic anhydride is produced and then hydrogenated in the presence of a copper-chromite catalyst to yield minor quantities of tetrahydrofuran and larger quantities of 1,4-butanediol and gamma-butyrolactone.
A more direct synthesis of tetrahydrofuran is proposed in British Patent Specification No. 1,293,151, which utilized a two component catalyst system to produce tetrahydrofuran from a solution of maleic anhydride or succinic anhydride in alcohol. The catalyst system is comprised of a hydrogenation catalyst containing copper and at least one other metal element and dehydration catalyst such as acid clay, molybdenum trioxide or silica alumina.
Lastly, tetrahydrofuran and gammabutyrolactone are derived from maleic anhydride or succinic anhydride using nickel base catalysts in U.S. Pat. No. 3,853,922 and U.S. Pat. No. 3,829,448.
The process described in British Patent Specification No. 1,293,151 provides yields of tetrahydrofuran in excess of 90%. However, the remainder of the above-mentioned processes or catalysts, typically results in low yields of tetrahydrofuran and the formation of relatively large amounts of by-products.
Therefore, an object of this invention is to provide a process for producing tetrahydrofuran in high yields while avoiding the formation of undesirable by-products. Another object is to provide an efficient catalyst with which tetrahydrofuran can be produced in high yields in a single hydrogenation step with less by-products. Still another object is to provide a process which can be carried out without the need for the high pressures and high temperatures required in the prior art processes. Still another object is to provide a novel hydrogenation catalyst system which maintains high activity over time.